Showing papers on "Detection limit published in 1987"

Detection limits with specified assurance probabilities

Abstract: Definition, estimation empirique et theorique, methodologie des limites de detection en analyse chimique

Determination of the rare-earth elements in geological materials by inductively coupled plasma mass spectrometry

Abstract: A method of analysis of geological materials for the determination of the rare-earth elements using the inductively coupled plasma mass spectrometric technique (ICP-MS) has been developed. Instrumental parameters and factors affecting analytical results have been first studied and then optimized. Samples are analyzed directly following an acid digestion, without the need for separation or preconcentration with limits of detection of 2-11 ng/g, precision of +/-2.5% relative standard deviation, and accuracy comparable to inductively coupled plasma emission spectrometry and instrumental neutron activation analysis. A commercially available ICP-MS instrument is used with modifications to the sample introduction system, torch, and sampler orifice to reduce the effects of high salt content of sample solutions prepared from geologic materials. Corrections for isobaric interferences from oxide ions and other diatomic and triatomic ions are made mathematically. Special internal standard procedures are used to compensate for drift in metal:metal oxide ratios and sensitivity. Reference standard values are used to verify the accuracy and utility of the method.

Determination of acetylcholine and choline in the femtomole range by means of HPLC, a post-column enzyme reactor, and electrochemical detection

Abstract: The measurement of choline and acetylcholine by means of HPLC, a post-column enzyme reactor, and electrochemical detection has been simplified and optimised. The use of a cation exchanger and enzyme reactor fitted in a cartridge holder appeared to result in reproducible, sensitive, and selective measurement of endogenous choline and acetylcholine with a lower detection limit of 50 fmole.

Chemiluminescence - High Performance Liquid Chromatography of Phosphatidylcholine Hydroperoxide

Abstract: A chemiluminescence - high performance liquid chromatography (CL-HPLC) system was developed for the hydroperoxide-specific detection of phosphatidylcholine hydroperoxide. In this system, chemiluminescence detector was equipped with normal phase HPLC. Luminol-cytochrome c solution was used as the hydroperoxide-specific luminescent reagent. A detection limit of 7 nmol hydroperoxide-O2 of phosphatidylcholine hydroperoxide could be achieved.

Determination of dissolved sulfide and sedimentary sulfur speciation using gas chromatography-photoionization detection

Abstract: The determination of dissolved sulfide and sedimentary sulfur is important to studies of trace element cycling in the aquatic environment A method employing selective generation of hydrogen sulfide, liquid-nitrogen-cooled trapping, and subsequent gas chromatographic separation/photoionization detection has been developed for such studies Dissolved sulfide is determined via acidification and gas stripping of a water sample, with a detection limit of 127 nM and a precision of 05% (relative standard deviation) With preconcentration steps, the detection limit is 013 nM Hydrogen sulfide is generated from sedimentary acid volatile sulfides (AVS) via acidification, from greigite using sodium borohydride and potassium iodide, and from pyrite using acidic chromium(II) The detection limit for these sulfur species is 61 mug of S/g, with the precision not exceeding 7% (relative standard deviation) This method is rapid and free of chemical interference, and field determinations are possible Numerous natural water and sediment samples have been analyzed by using the described procedures

Elemental speciation via high-performance liquid chromatography combined with inductively coupled plasma atomic emission spectroscopic detection: application of a direct injection nebulizer

Abstract: An evaluation is presented of a direct injection nebulizer (DIN) interfaced to a high-performance liquid chromatograph (HPLC) with inductively coupled plasma atomic emission spectroscopic (ICP-AES) detection for simultaneous multielement speciation. The limits of detection (LODs) obtained with the DIN interface in the HPLC mode were found to be comparable to those obtained by continuous-flow sample introduction into the ICP, or inferior by up to only a factor of 4. In addition, the DIN allowed for the direct injection into the ICP of a variety of common HPLC solvents (up to 100% methanol, acetonitrile, methyl isobutyl ketone, pyridine, and water). The HPLC-DIN-ICP-AES system was compared to other HPLC-atomic spectroscopic detection techniques and was found to offer substantial improvement over the alternative on-line, detection methods in terms of LODs. Representative applications of the HPLC-DIN-ICP-AES system to the elemental speciation of coal process streams, shale oil, solvent refined coal, and crude oil are presented.

Polycyclic aromatic hydrocarbons in soil and air: statistical analysis and classification by the SIMCA method

Abstract: Soil samples from 12 locations in Norway have been analyzed for 9 polycyclic aromatic hydrocarbons (PAH). The same unsubstituted PAH have been determined in air samples collected near an aluminum reduction plant. Analysis by high-resolution gas chromatography-mass spectroscopy in the selected ion mode showed concentrations in soil ranging from less than 1 ppb (detection limit) to 993 ppb for individual unsubstituted PAH. The highest concentrations are found close to aluminum plants. Correlation analysis and SIMCA pattern recognition show that the patterns of unsubstituted PAH in soils samples collected close to aluminum plants are different from those in soil samples collected from other areas. Soil samples from a bog environment show a somewhat different pattern of PAH than other soil samples. 43 references, 6 figures, 5 tables.

Determination of retinol, alpha-tocopherol, and beta-carotene in serum by liquid chromatography with absorbance and electrochemical detection.

Abstract: We describe a method for the determination of retinol, alpha-tocopherol, and beta-carotene in serum, using a liquid-chromatographic separation with wavelength-programmed ultraviolet/visible absorbance and amperometric electrochemical detection with a glassy carbon electrode. After protein denaturation and addition of an internal standard, tocol, 250-microL samples are twice extracted with hexane. The reversed-phase, gradient-elution chromatographic separation provides baseline resolution of: the all-trans isomer of retinol from the cis isomers, alpha- from gamma-tocopherol, and all-trans-beta-carotene from alpha-carotene and from cis-beta-carotene isomers. The linearity of response and the detection limits for the two detectors for the three analytes are measured. A comparison of the values obtained for serum extracts shows good agreement between the absorbance and electrochemical detectors.

Determination of picomolar levels of cobalt in seawater by flow injection analysis with chemiluminescence detection

Abstract: Flow injection analysis (FIA) was used to automate the determination of cobalt in seawater by the Co-enhanced chemiluminescent oxidation of gallic acid in alkaline hydrogen peroxide. A preconcentration/separation step in the FIA manifold with an in-line column of immobilized 8-hydroxyquinoline was included to separate the Co from alkaline-earth ions. One sample analysis takes 8 min, including the 4-min sample load period. The detection limit is approximately 8 pM. The average standard deviation of replicate analyses at sea of 80 samples was +/- 5%. The method was tested and intercalibrated on samples collected off the California coast.

Preparation of biological tissue for determination of arsenic and selenium by graphite furnace atomic absorption spectrometry

Abstract: A great deal of interest has been generated in the measurement of selenium in biological tissue. Consequently, a method was needed for the digestion of large numbers of tissue samples (mainly eggs and liver of avian species) for arsenic and selenium analysis. Several wet digestion methods are described for the solubilizing of biological tissues and perchloric acid is often used in these procedures. However, this acid can be dangerous and particularly so in the presence of organic material. To avoid the use of perchloric acid, the authors have used an open flask digestion method which involves the careful evaporation of a 20-mL nitric acid/tissue solution down to 3 mL, directly on a hot plate. The authors have overcome many of the shortcomings of this method through a modification of the nitric acid digestion method in which hydrogen peroxide is added during the digestion process to enhance the solubilizing of the biological tissue. Samples solubilized in this manner were then quantified directly for arsenic and/or selenium by using graphite furnace atomic absorption spectrometry (GFAAS) with Zeeman background correction. The authors were able to have the method for selenium independently verified by stable isotope dilution mass spectrometry (SIDMS). The lower limit ofmore » detection, based on a 0.5-g subsample (wet weight) and a 25-mL final volume dilution, was 0.10 pp for both arsenic and selenium. The lower limit of detection, based on a 0.25-g subsample (dry weight) and a 50-mL final volume dilution, was 0.40 ppm for the two elements.« less

Fluorometric determination of hydrogen peroxide in groundwater

Abstract: The fluorometric scopoletin-horseradish peroxidase method has been modified for field determinations of hydrogen peroxide concentrations in groundwaters. Standard additions calibration compensates for background fluorescence and inconsistent stoichiometry of the fluorescence quenching reaction due to interferences by the matrix. The detection limit, defined as the blank plus three standard deviations, ranged from 3.6 to 44.6 nM. However, this limit was more an indication of the difficulty of preparing peroxide-free water than the actual limit imposed by the sensitivity of the method for the peroxide contamination introduced with the reagents. For 111 field determinations the weighted average (uncorrected) hydrogen peroxide concentration was 20.2 nM and the pooled standard deviation was 7.7 nM. The average of 45 field blanks was 7.8 nM with a pooled standard deviation of 5.2 nM. At nanomolar concentration levels, it is essential that samples are analyzed for H/sub 2/O/sub 2/ in the field. Storage periods exceeding 1 h caused serious errors and irreproducible results.

Absorption spectroscopy at the limit: detection of a single atom.

Abstract: We investigate the sensitivity limit of absorption spectroscopy. An experiment is described in which the decrease in transmitted light intensity that is due to absorption by a single, electromagnetically confined atomic ion is observed.

Flow injection chemiluminescence determination of sulphite

Abstract: A comparison is made of the use of riboflavin and 3-cyclohexylaminopropanesulphonic acid (CAPS) to increase the sensitivity of the determination of sulphite in a flow injection procedure based on the chemiluminescence produced by permanganate oxidation in an acidic solution. Both procedures give linear calibration graphs for 5–60 ng of sulphite, but the CAPS procedure has a lower detection limit (1.2 ng) and better relative standard deviation (RSD)(2.5% for 40 ng, n=10). Riboflavin enhancement arises from energy transfer, but the reason for the CAPS enhancement could not be identified with certainty.

Surface enhanced Raman spectrometry on silver hydrosols studied by flow injection analysis

Abstract: Surface enhanced Raman scattering (SERS) corresponds to the increase of the Raman scattering cross section of organic molecules (five to six orders of magnitude) when molecules are adsorbed onto metal surfaces. The use of silver hydrosols, obtained by chemical reduction of silver nitrate solutions, is convenient. An important drawback is irreproducibility of hydrosol preparation procedures and the nonlinearity between the SERS response and the analyte concentration. In order that these problems could be overcome, flow injection analysis (FIA) has been used. With FIA, constant, reproducible silver hydrosol formation results. SERS signals of para-aminobenzoic acid (PABA) were measured over four orders of magnitude of concentration range and over three pH units. The precision of FIA-SERS signals for PABA was 5%, and the limit of detection of PABA was in the ppb range with the use of the Raman band at 1605 cm−1 with an Ar+ laser at 514.5 nm.

Determination of morphine in body fluids by high-performance liquid chromatography with chemiluminescence detection.

Abstract: HPLC has been used in combination with chemiluminescence detection for the determination of morphine in biological fluids. Solid-liquid extraction procedures for the isolation of morphine from whole blood and urine are described, as is the synthesis of the internal standard, N-ethylnormorphine. Improved selectivity and sensitivity over UV detection is apparent. The procedure has a detection limit of 5 ng of morphine on-column after extraction from blood or urine. The utility of the procedure has been tested on forensic case samples.

Cleaning of MBE GaAs Substrates by Hydrogen Radical Beam Irradiation

Abstract: Hydrogen radical beam cleaning of substrates for GaAs MBE growth has been studied. The cleaning effects of carbon and oxygen contaminated by exposure to air and a lower-grade vacuum were investigated using Auger electron spectroscopy (AES), capacitance-voltage (C-V) carrier profiling, and secondary ion mass spectrometry (SIMS). AES signals of contaminants decreased to the detection limit with hydrogen radical irradiation. Carrier depletion around the growth interface was also reduced with decreasing carbon density.

Inductively Coupled Plasma-Mass Spectrometry For Elemental Analysis and Isotope Ratio Determinations in Individual Organic Compounds Separated by Gas Chromatography

Abstract: A gas chromatograph (GC) with a packed column was interfaced to an inductively coupled plasma-mass spectrometer (ICP-MS) to yield atomic mass spectra from volatile organic compounds. Atomization of injected compounds was nearly complete and independent of molecular structure, so that elemental ratios could be determined. Detection limits were in the range 0.001 to 400 ng s−1, depending on the ionization energy of the element and its abundance in the background spectrum. The relative standard deviation of measured isotope ratios varied from 0.4% for Br (i.e., a ratio close to unity) to 18% for N (a very large ratio). Thus, GC-ICP-MS provides elemental and isotope ratio information that is complementary to the molecular information derived from GC-MS with conventional ionization methods.

Performance of a glow discharge mass spectrometer for simultaneous multielement analysis of steel

Abstract: The analysis of steel has been performed on a previously described laboratory prototype of a new glow discharge mass spectrometry (GDMS) system equipped with a quadrupole filter in order to study its analytical performance. Operational parameters of the discharge have been optimized and seven NBS standards and one USS standard have been analyzed. A weighted regression has been applied for calibration. The results include sensitivity factors and precision data for 26 elements. In multielement analysis, the detection limit was about 0.1 mol/mol while single-element determination was possible at a 5 times lower detection limit. Analysis results for two test samples with 30 elements each agree within 10% of the certified values. Consequently the method proves to be a valuable tool for simultaneous multielement trace analysis of solids.

High Performance Liquid Chromatographic Determination of Amino Acids in Biological Samples by Precolumn Derivatization with O-Phthaldialdehyde

Abstract: A suitable gradient system has been developed for rapid analysis of amino acids in biological samples using O-phthaldialdehyde as a precolumn derivatizing agent and fluorescence detection. Resolution of 21 amino acids has been accomplished with 3 μm Ultrasphere ODS column by using a multi-step gradient system of two solvents (0.1M sodium acetate, pH 7.2/methanol:tetrahydrofuran) in less than 1 hour. Within-assay and between-assay coefficients of variation of retention times and fluorescence yield show good reproducibility. The fluorometric detection response is linear from 25 to 500 pmoles with a minimum detection limit of less than 1 pmol. High resolution, rapid analysis and high sensitivity of this method facilitates amino acid analysis in samples of less than 1 mg of tissue.

Separation of Amino Acid Enantiomers Using Precolumn Derivatization with o-Phthalaldehyde and 2,3,4,6-Tetra-O-acetyl-1-thio-β-glucopyranoside

Abstract: A method is described for resolution of amino acid enantiomers. The D- and L-amino acids were reacted with o-phthalaldehyde (OPA) and the optically active 2,3,4,6-tetra-O-acetyl-1-thio-β-glucopyranoside (TATG). The reaction was complete in a few minutes at room temperature and the derivatives were quite stable. The formed diastereomers were separated by reversed phase chromatography and the selectivity was generally good, except for lysine and ornithine. A mean separation factor (α) of 1.27 was obtained with acetonitrile as an organic modifier. The fluorescence excitation and emission maxima were at 342 nm and 410 nm respectively, and the electrochemical half-wave potential E½ ≡ 0.65–0.75 V. The detection limits (for L-leucine) were 23 pmol and 1 pmol (S/N 3:1) in the respective detection modes. With laser-induced fluorescence detection (He-Cd laser, 325 nm) and microcolumns, a detection limit in the fmol range is obtainable.

Glow discharge mass spectrometry ― a powerful technique for the elemental analysis of solids

Abstract: A high resolution glow discharge mass spectrometer for the elemental analysis of solids is described. The analytical performance is reviewed and results are presented on a wide range of materials illustrating elemental and concentration coverage, quantitation and detection limits. Comparisons with other techniques are made.

Determination of Mercury in Geological Materials by Continuous-Flow, Cold-Vapor, Atomic Absorption Spectrophotometry

Abstract: To determine mercury in geological materials, samples are digested with nitric acid and sodium dichromate in a closed teflon vessel. After bringing to a constant weight, the digest is mixed with air and a sodium chloride-hydroxylamine hydrochloride-sulfuric acid solution and then Hg(II) is reduced to Hg/sup 0/ with stannous chloride in a continuous flow manifold. The mercury vapor is then separated and measured using cold vapor atomic absorption spectrophotometry (CV-AAS). For a 100 mg sample the limit of detection is 20 parts-per-billion (ppb) Hg in sample. To obtain a 1% absorption signal, the described method requires 0.21 ppb Hg solution (equal to 16 ppb in sample). Precision is acceptable at less than 1.2% RSD for a 10 ppb Hg aqueous standard. Accuracy is demonstrated by the results of the analysis on standard reference materials. Several elements do interfere but the effect is minimal because either the digestion procedure does not dissolve them (e.g., Au or Pt) or they are normally of low abundance (e.g., Se or Te).

Ultrasensitive laser-induced fluorescence detection in hydrodynamically focused flows

Abstract: The detection sensitivity for fluorescent species in hydrodynamically focused flows has been significantly enhanced. Improved flow parameters, efficient detection optics, and photon counting are the keys to this enhancement. A detection limit of 800 Rhodamine 6G molecules flowing through our 0.6-pL probe volume during a 1-sec counting interval has been achieved. At the detection limit, the probability of a Rhodamine 6G molecule’s being in the probe volume is 0.06. Our current apparatus is capable of detecting a single species containing the equivalent of eight Rhodamine 6G fluorophores during the passage of this species through the focused laser beam. A number of instrumental improvements are being implemented that will further enhance the detection sensitivity projected to the limit of a single molecule.